Real-time collection of navigation and other relevant downhole data at a drill bit and transmission of the data to a surface rig is a common practice in off-shore and land-based drilling rigs. This technology has been called “Measurement-While-Drilling” (MWD). Logging data may also be transmitted uphole, and if so, the technology is referred to as Logging-While-Drilling (LWD).
Current commercialized MWD and LWD technologies include mud pulse telemetry, in which pressure pulses are generated in the mud by periodically constricting the flow through the drill string. However, the data transmission rates using mud pulse telemetry are slow (<1 binary bit/second), which limits the type of data that can be usefully collected. Wireline telemetry has been used in the industry, and provides greater data throughput than mud pulse telemetry, but electric cables that are used to transmit data up and down the drill string are vulnerable to damage and impose limitations to the operation of the drill string.
Wireless telemetry technology other than mud pulse telemetry has been developed that avoids the physical limitations of wireline cables and has a higher data transmission throughput than mud-pulse telemetry. Examples of wireless telemetry include electromagnetic telemetry, in which signals are sent as electromagnetic waves through the Earth. Electromagnetic Telemetry is limited to operating in areas where the formation resistivity is in an acceptable range to allow transmission.
Another type of wireless telemetry is acoustic telemetry, which involves the transmission of data with acoustic energy through such mediums as drill pipe. Acoustic telemetry applications include MWD, LWD, drill-stem-testing (DST), production, downhole pump performance, smart well completions, utility crossings and river crossings.
Several technological challenges exist with implementing acoustic telemetry technology in these applications. The complex wave physics associated with this type of data transmission require careful consideration to the design of the components of an acoustic telemetry system, which include a downhole sensor pack and transmitter, and an above-surface receiver. Technical challenges exist in ensuring that the above-surface receiver receives an acoustic signal with measurable strength and quality, and that the components of the telemetry system are robust, affordable and compatible with the drilling operation.
As an example, U.S. Pat. No. 6,320,820 describes an acoustic telemetry system in which an “acoustic telemetry receiver” is coupled to a kelly to receive transmitted telemetry signals. The telemetry receiver in this instance is a wired device, and thus cannot be used while tubulars are rotating. It is also bulky, limiting its placement on the drillstring to locations that may not be acoustically optimal.
Another application of acoustic telemetry technology in the drilling industry is above-ground acoustic monitoring of downhole acoustic signals from sources other than an acoustic transmitter. Monitoring applications include receiving timing information for seismic-while-drilling (SWD), monitoring drilling dynamics, air hammer monitoring, fluid hammer monitoring, casing drilling, and bottom hole assembly (BHA) retrieval and seating confirmation.
Examples of published monitoring systems includes the Advanced Drillstring Analysis and Measurement System (ADAMS) published in IADC/SPE paper 19998 and SPE paper 14327. The ADAMS comprises a measurement sub, a wireless telemetry system, and an instrumented trailer laboratory. The measurement sub must be inserted into the drillstring, to form a structural component, and is thus intrusive and not compatible with various drill collar connections without additional cross-over subs. This requires additional rig time to install, adds potential failure points, adds additional wear and tear to the drill string components, and affects rig operations such as pumping.
It is therefore desirable to provide an acoustic telemetry system that improves on at least some of the deficiencies of the state of the art.